1. Field of the Invention
The present invention relates in general to the control of the dust suction force of a vacuum cleaner, and more particularly to an apparatus and method for controlling the speed of a suction motor in a vacuum cleaner, wherein the speed of the suction motor, corresponding to the dust suction force of the vacuum cleaner, can automatically be controlled according to amount of dust on floors, carpets and the like to be cleaned.
2. Description of the Prior Art
Referring to FIG. 1, there is shown, in block form, an example of conventional apparatus for controlling the speed of a suction motor in a vacuum cleaner. As Shown in FIG. 1, the conventional apparatus comprises an infrared transmitter 3 disposed at one side in a suction port 1 (see FIG. 3) of the vacuum cleaner for transmitting infrared rays, an infrared receiver 4 disposed at the opposite side in the suction port 1 for receiving the infrared rays from the infrared transmitter 3 and ouputting electrical signals corresponding to amount of the sucked dust in accordance with amount of the received infrared rays, a differentiator 5 for differentiating output signals from the infrared receiver 4, a comparator 6 for comparing the output signal from the differentiator 5 with a reference voltage and reshaping the compared signal into a rectangular pulse, and a control circuit 7 for counting up the number of the output pulses from the comparator 6 during a sampling time and controlling the speed of a suction motor 8 (see FIG. 2) in accordance with the total number of the pulses.
Referring to FIG. 2, there is shown a detailed block diagram of the control circuit 7 in the apparatus of FIG. 1. As shown in this drawing, the control circuit 7 includes a pulse number counter 71 for counting up the number of the output pulses from the comparator 6 during the sampling time, a predetermined time controller 72 for controlling the sampling time during which the pulse number counter 71 counts up the number of the output pulses from the comparator 6, a speed rate calculator 73 for calculating a speed rate based on the total number of the pulses, a firing angle controller 74 for controlling a firing angle in accordance with the calculated speed rate from the speed rate calculator 73 to control the rotational speed of the suction motor 8, and a speed display controller 75 for controlling a display 9 which displays the current speed, in accordance with the calculated speed rate from the speed rate calculator 73.
The operation of the conventional apparatus for controlling the speed of the suction motor in the vacuum cleaner, constructed as mentioned above, will hereinafter be described.
As mentioned previously, the infrared transmitter 3 and the infrared receiver 4 cooperate to detect the amount of the sucked dust. As shown in FIG. 3, the infrared transmitter 3 and the infrared receiver 4 are disposed oppositely to each other at both sides of the suction port 1 of the vacuum cleaner. In this construction, the amount of infrared rays which the infrared receiver 4 receives from the infrared transmitter 3 is in inversely proportional to the amount of the dust 2 being sucked through the suction port 1. In other words, the more the amount of dust being sucked, the less infrared light received by the light receiving transistor in the infrared receiver 4. Consequently, the potential at the collector of the light receiving transistor rises. In other words, the infrared rays from the infrared transmitter 3 are blocked by foreign substances such as the sucked dust 2 wastepapers, or the like, causing the light receiving transistor in the infrared receiver 4 to be turned off. The turning-off of the light receiving transistor results in an output of a high level voltage signal therefrom.
The output voltages produced dependently on the amount of the sucked dust in the infrared receiver 4 are differentiated by the differentiator 5 and then applied to the comparator 6 for comparison with a predetermined reference voltage. As a result of the comparison, outputted from the comparator 6 are rectangular pulse signals in which high level pulse intervals and low level pulse intervals can be definitely distinguished, as shown in FIG. 4. The low level pulse intervals of the pulse signals indicate that dust is not being sucked, while the high level pulse indicate that dust is being sucked. It can be immediately found that the more dust being sucked is, the more frequent high level pulses are generated.
On the other hand, the control circuit 7 counts the number of the output pulses from the comparator 6 during the predetermined period of time and controls the rotational speed of the suction motor 8 in accordance with the total number of the pulses counted during the predetermined period of time. That is, in the control circuit 7, the pulse counter 71 is enabled during the sampling time under the control of the predetermined time controller 72. As a result, the pulse counter 71 counts up the number of the pulses which are fed from the comparator 6 during the predetermined period of time. In the speed control value calculator 73, the speed control value is calculated based on the total number of pulses counted by the pulse counter 71. The speed control value then calculator applied to the firing angle controller 74. As a result, the firing angle controller 74 controls the firing angle of the suction motor 8, in accordance with the speed control value calculated from the speed control value calculator 73, to adjust the rotational speed of the suction motor 8 and the dust suction force of the vacuum cleaner. At this time, the speed display controller 75 controls the display 9 to indicate the speed or the amount of the dust being sucked in accordance with the calculated speed control value from the speed control value calculator 73. Upon checking the speed of the suction motor, the user may figure out the amount of the dust being sucked since the speed of the suction motor corresponds to the amount of the dust being sucked.
However, the above-mentioned conventional apparatus fails to take into account the fact that the longer the high level pulse time is, the more the amount of dust is being sucked. As a result, the conventional apparatus has a disadvantage, in that it cannot properly cope with the size and amount of the sucked dust, since it merely counts the pulses detected during the predetermined period of time and controls the speed of the suction motor, regardless of the pulse time or how the high level pulses are.
Recently, there have been proposed apparatuses for controlling the rotation speed of the motor in consideration of the size of the sucked dust.
A representative example of such an apparatus is shown in Korean Patent Laid-open Publication No. 90-17542 (Korean Patent Application No. 90-6698, filed May 11, 1990). This representative apparatus comprises dust detecting means for transforming output signals from a dust detecting sensor into pulse signals and control means for counting the number of output pulses from the dust detecting means during a predetermined period of time. It then applies a pulse width correction to the counted total number of pulses and controls the rotational speed of the suction motor in accordance with the compensated total number of pulses.
For example, assume that n is the counted number of the pulses, at least one of which has a wide pulse width. In this case, the correction of the number n pulses is obtained by multiplying the number n by a pulse width correction coefficient k (n.times.k). Therefore, the speed of the suction motor in the vacuum cleaner is controlled according to the compensated number of the pulses.
Such a conventional apparatus suggests a compensation with respect to a pulse width, however, it requires extra steps and components for comparing each pulse width with a reference pulse with respect to their pulse width, and selecting out a desirable pulse width compensation coefficient while taking into account how many wide pulses are among the total high level pulse and how wide they are.